THE ALG^-FUNGI (PHYCOMYCETES) 217 



If bread that has not been exposed to the air is cut in a 

 room in which the air is quiet, and if one piece is covered 

 directly in a glass dish, another similarly covered after five 

 minutes' exposure to the air of the room, and aliother after 

 five minutes' exposure on the outside window sill, an interest- 

 ing test of the abundance of spores in the atmosphere will be 

 afforded. One class of students, 

 in performing this experiment, 

 secured the development of mold 

 upon all three pieces of bread, 

 having in all five kinds of mold. 



204. Bread mold : sexual re- 

 production. Bread mold rarely 

 reproduces itself by sexual proc- 

 esses, but does so under some 

 circumstances. The tips of hy- 

 phse approach one another, and 

 end cells are formed by means 

 of transverse walls. These end 

 cells gradually unite to produce 

 a spore, and a heavy dark wall 

 is formed about it.. Since this 

 spore is produced by the union 

 of similar cells it is called a zy- 

 gospore. It is a well-protected 

 spore, and seems fitted for en- 

 during great extremes in physical conditions. The germi- 

 nation of the zygospore of Rhizopus nigricans is an occurrence 

 that is difficult to demonstrate in the laboratory, though it 

 and closely related molds (Mucor mucedo and Sporodinia) form 

 zygospores that have been seen to germinate and thus repro- 

 duce the mold plants. The similarity between the formation 

 of zygospores in molds and in Spirogyra is worthy of note. 



205. Water mold (Saprolegnia). Although there are several 

 kinds of water molds, this is the most common one. It lives 

 in the water, upon dead insects, fish, and other animals. 



FIG. 177. Water mold growing on 

 the body of a wasp 



The fungus has grown upon the host 



until an extensive white fluffy mass 



has been formed 



